Switching device and electronic circuit

ABSTRACT

A switching device  1  includes a SiC semiconductor chip  11  which has a gate pad  14 , a source pad  13  and a drain pad  12  and in which on-off control is performed between the source and the drain by applying a drive voltage between the gate and the source in a state where a potential difference is applied between the source and the drain, a sense source terminal  4  electrically connected to the source pad  13  for applying the drive voltage, and an external resistance (source wire  16 ) that is interposed in a current path between the sense source terminal  4  and the source pad  13 , is separated from sense source terminal  4 , and has a predetermined size.

FIELD OF THE INVENTION

The present invention relates to a switching device using SiC and anelectronic circuit comprising the same (for example, inverter circuit,converter circuit and the like).

BACKGROUND ART

A switching device used for an electronic circuit such as an invertercircuit, a converter circuit and the like is generally configured from aplurality of switching elements connected in parallel to increase anelectric capacity. An SiC switching element is known as a switchingelement along with an Si switching element. An SiC switching elementincludes, for example, SiC-MOSFET (Metal-Oxide-Semiconductor FieldEffect Transistor), SiC-bipolar transistor (Bipolar Transistor),SiC-JFET (Junction Field Effect Transistor), SiC-IGBT (Insulated GateBipolar Transistor), and the like.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: Japanese Unexamined Patent Publication No.    2005-137072

OUTLINE OF THE INVENTION Subject to be Solved by the Invention

In an electronic circuit to which an SiC switching device (MOSFET) isincorporated, when, for example, a power-supply voltage is directlysupplied to the device thereby to cause a short circuit, an overcurrent(short-circuit current) may flow through the device. In this case, whilethis short-circuit current is blocked by connecting a gate terminal ofthe device to ground, a certain time is required before blocking. Forexample, it takes around 10 μsec (microsecond) after the overcurrent isdetected.

However, if an overcurrent cannot be blocked within a short-circuitcapacity of each device, thermal destruction of the device may be causeddue to thermal runaway by the short-circuit current.

An object of the present invention is to provide a switching devicehaving a low impact on a switching performance of a switching elementand being capable of improving a short-circuit capacity of the device aswell as an electronic circuit comprising the same.

SUMMARY OF THE INVENTION

A switching device according to the invention includes a SiC switchingelement which has a first electrode, a second electrode and a thirdelectrode and in which on-off control is performed between the secondelectrode and the third electrode by applying a drive voltage betweenthe first electrode and the second electrode in a state where apotential difference is applied between the second electrode and thethird electrode, a drive terminal electrically connected to the secondelectrode for applying the drive voltage, and an external resistancethat is interposed in a current path between the drive terminal and thesecond electrode, is separated from at least one of the drive terminaland the second electrode, and has a predetermined resistance value.

According to this configuration, the external resistance is interposedin series in the current path between the drive terminal and the secondelectrode. Thus, a voltage applied between the first electrode and thesecond electrode when an overcurrent flows between the second electrodeand the third electrode can be reduced by a voltage drop at thisexternal resistance in comparison to a case where the first electrodeand the second electrode are directly connected by a bonding wire or thelike to form this current path. As a result, a short-circuit capacity ofthe device can be increased.

On the other hand, by properly setting a resistance value of thisexternal resistance, the voltage drop at this external resistance can bereduced when a current flowing between the second electrode and thethird electrode is relatively small or is a rated value. In this case, areduction of the voltage applied between the first electrode and thesecond electrode can be suppressed, and a drive voltage necessary andsufficient for a switching operation can be fed to a switching element.That is, an impact on a switching performance of the switching elementcan be small.

One embodiment of the present invention includes an output terminal foroutputting a current flowing by the on control and a conductive memberconnecting the output terminal and the second electrode, and theexternal resistance includes the conductive member.

According to this configuration, since the conductive member for currentoutput is used as the external resistance, the effect of theabove-described improvement of the short-circuit capacity can beachieved with a low cost without the number of components increased.

One embodiment of the present invention includes the conductive memberincludes a bonding wire stretched between the output terminal and thesecond electrode.

According to this configuration, a resistance value of the bonding wireis a value previously fixed by its constituent material, length, wirediameter and the like. Thus, the resistance value of the externalresistance can be easily adjusted by appropriately increasing anddecreasing the number of wires between the output terminal and thesecond electrode.

One embodiment of the present invention includes a resin package sealingthe SiC switching element, the drive terminal and the externalresistance.

According to this configuration, since the external resistance is sealedby the resin package, the switching device can be installed with aconventional layout.

In one embodiment of the present invention, the first electrode is agate electrode, the second electrode is a source electrode, the thirdelectrode is a drain electrode, and the drive terminal is a sense sourceterminal. That is, the switching device of the present invention may bea MOSFET.

In one embodiment of the present invention, the first electrode is agate electrode, the second electrode is an emitter electrode, the thirdelectrode is a collector electrode, and the drive terminal is a senseemitter terminal. That is, the switching device of the present inventionmay be an IGBT.

In one embodiment of the present invention, the first electrode is abase electrode, the second electrode is an emitter electrode, the thirdelectrode is a collector electrode, and the drive terminal is a senseemitter terminal. That is, the switching device of the present inventionmay be a bipolar transistor.

An electronic circuit of the present invention includes the switchingdevice of the present invention, an overcurrent detection circuit fordetecting that an overcurrent is flowing through the switching device,and an overcurrent protection circuit for blocking the current flowingthrough the switching device when an overcurrent is detected by theovercurrent detection circuit.

According to this configuration, an electronic circuit can be providedwhich has a small impact on a switching performance of the switchingelement and can improve the short-circuit capacity of the switchingdevice since it comprises the switching device of the present invention.

The above-described and other objects, features and effects of thepresent invention are revealed by the following embodiments described inreference to accompanied drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a switching device according to oneembodiment of the present invention.

FIG. 2 is an electrical circuit diagram of the switching device in FIG.1 .

FIG. 3 is an electrical circuit diagram of an inverter circuit accordingto one embodiment of the present invention.

FIG. 4 is an electrical circuit diagram showing an electricalconfiguration of a module to which a plurality of the switching devicesin FIG. 1 are installed.

FIG. 5 is an electrical circuit diagram showing an electricalconfiguration of a gate drive circuit.

FIG. 6 is a graph showing a relation between a gate-to-source voltage ofthe switching devices in FIG. 1 and a short-circuit capacity.

FIG. 7 is a plan view for illustrating a configuration of asemiconductor module.

FIG. 8 is a schematic sectional view along a line VIII-VIII in FIG. 7 .

FIG. 9 is a schematic sectional view along a line IX-IX in FIG. 7 .

FIG. 10 is an electrical circuit diagram showing an electricalconfiguration of the semiconductor module in FIG. 7 .

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention is described below in detailreferring to the drawings.

FIG. 1 is a schematic view of a switching device 1 according to oneembodiment of the present invention. FIG. 2 is an electrical circuitdiagram of the switching device 1 in FIG. 1 . In FIG. 1 , to clarify theconfiguration of the switching device 1, one corner portion (broken-linehatched area) of a semiconductor chip 11 is shown transparently.

The switching device 1 includes a resin package 2 having a flatrectangular-parallelepiped shape, a source terminal 3 (S) that is sealedon the resin package 2 and serves as an example of an output terminal ofthe present invention, a sense source terminal 4 (SS) as an example of adrive terminal of the present invention, a gate terminal 5 (G) and adrain terminal 6 (D).

The four terminals 3 to 6 are respectively formed of a metal plate in apredetermined shape, and are arranged in order from one side surface ofthe resin package 2 to a side surface opposed to it.

In this embodiment, each of the source terminal 3 and the drain terminal6 is formed in a shape including islands 7, 8 in a rectangle shape andterminal portions 9, 10 in an elongated rectangle shape extendinglinearly from one side of these islands 7, 8. The sense source terminal4 and the gate terminal 5 are formed in an elongated rectangle shapesimilar to the terminal portions 9, 10. The terminal portion 9 of thesource terminal 3, the sense source terminal 4, the gate terminal 5, andthe terminal portion 10 of the drain terminal 6 are arranged so as to beparallel one another.

The semiconductor chip 11 as an example of an SiC switching element ofthe present invention is placed on the drain terminal 6 (center portionof the island 8). An almost entire rear surface of the semiconductorchip 11 is provided with a drain pad 12 as an example of a thirdelectrode of the present invention, and this drain pad 12 is joined tothe island 8. Thus, the drain pad 12 of the semiconductor chip 11 andthe drain terminal 6 are electrically connected. A front surface of thesemiconductor chip 11 is provided with a source pad 13 as an example ofa second electrode of the present invention and a gate pad 14 as anexample of a first electrode of the present invention.

The source pad 13 has a generally square shape in a plan view, and isformed in a manner to cover almost an entire region of the front surfaceof the semiconductor chip 11. The source pad 13 is provided with aremoval region 15 in a vicinity of a center of its one side. The removalregion 15 is not provided with the source pad 13. The gate pad 14 isdisposed on the removal region 15. The gate pad 14 and the source pad 13are spaced apart and are insulated from each other.

A plurality of source wires 16 (bonding wires) are stretched as anexample of a conductive member of the present invention between thesource pad 13 and the source terminal 3, and the source pad 13 and thesource terminal 3 are electrically connected by the source wires 16. Inthis embodiment, four source wires 16 having the same length arearranged parallel to each other. Thus, a resistance of each source wire16 can be unified to a constant value. Further, a sense source wire 17(bonding wire) is stretched between the source terminal 3 (island 7) andthe sense source terminal 4. Thus, the sense source terminal 4 iselectrically connected to the source pad 13 via a current path includingthe sense source wire 17 and the source wires 16.

Thus, instead of directly connecting the sense source terminal 4 and thesource pad 13 by a conventional wire 21 shown in FIG. 1 with a brokenline, one end of the sense source wire 17 is separated from the sourcepad 13 and is connected to the source terminal 3. As a result, as shownin FIG. 2 , an external resistance 22 having a resistance value rdepending on a constituent material, a length, a wire diameter and thelike of the source wire 16 can be connected in series between the sensesource terminal 4 and the source pad 13. That is, in the switchingdevice 1 according to this embodiment, a position of the sense source isspaced from a source end (source pad 13) of the semiconductor chip 11,and a wire, wiring and the like intervene therebetween, whereby anexternal gate resistance (external resistance 22) which serves as aparasitic resistance when the gate-to-source voltage is applied to thesemiconductor chip 11 is provided.

A gate wire 18 (bonding wire) is stretched between the gate pad 14 andthe gate terminal 5, and the gate pad 14 and the gate terminal 5 areelectrically connected by the gate wire 18.

Further, in this embodiment, as shown in FIG. 2 , the semiconductor chip11 includes a MOSFET 19 using SiC (SiC-MOSFET) and a body diode 20. Asource, a drain and a gate of the MOSFET 19 are electrically connectedto the source pad 13, the drain pad 12 and the semiconductor chip 11,respectively. The switching element formed in the semiconductor chip 11may be an element other than a MOSFET. For example, this switchingelement may be SiC-IGBT, a SiC-bipolar transistor, SiC-JFET and thelike. When the switching element is SiC-IGBT, the source pad 13, thedrain pad 12, the gate pad 14 and the sense source terminal 4respectively correspond to an emitter pad, a collector pad, a gate padand a sense emitter terminal of a SiC-IGBT. When the switching elementis a bipolar transistor, the source pad 13, the drain pad 12, the gatepad 14 and the sense source terminal 4 respectively correspond to anemitter pad, a collector pad, a base pad and a sense emitter terminal ofa SiC-bipolar transistor.

Further, the resin package 2 seals the semiconductor chip 11, therespective entire wires 16 to 18, the entirety of the island 7 and partof the terminal portion 9 of the source terminal 3, part of each of thesense source terminal 4 and the gate terminal 5, as well as the entireisland 8 and part of the terminal portion 10 of the drain terminal 6.Parts of the terminal portion 9 of the source terminal 3, the sensesource terminal 4, the gate terminal 5 and the terminal portion 10 ofthe drain terminal 6 are exposed respectively.

FIG. 3 is an electrical circuit diagram of an inverter circuit 31according to an embodiment of the present invention. FIG. 4 is anelectrical circuit diagram showing an electrical configuration of aswitching module 43 to which a plurality of the switching devices 1 inFIG. 1 are installed.

The inverter circuit 31 as an example of an electrical circuit of thepresent invention includes first to fourth switching devices 32 to 35,first to fourth gate drive circuits 36 to 39, and a control section 40.

The first to fourth switching devices 32 to 35 are respectivelyconfigured from the above-described switching devices 1. FIG. 3selectively shows from the circuit elements in FIG. 2 what are necessaryfor illustration of FIG. 3 . Further, as the first switching device 32is shown as a representative example in FIG. 4 , for example, the firstto fourth switching devices 32 to 35 may be incorporated into theinverter circuit 31 as the switching module 43 configured by parallellyconnecting a plurality of the switching devices 1.

A drain terminal 6 of the first switching device 32 is connected to apositive electrode terminal of a power supply 41. A source terminal 3 ofthe first switching device 32 is connected to a drain terminal 6 of thesecond switching device 33. A gate terminal 5 of the first switchingdevice 32 and a sense source terminal 4 of the first switching device 32are connected to the first gate drive circuit 36.

A source terminal 3 of the second switching device 33 is connected to anegative electrode terminal of the power supply 41. A gate terminal 5 ofthe second switching device 33 and a sense source terminal 4 of thesecond switching device 33 are connected to the second gate drivecircuit 37.

A drain terminal 6 of the third switching device 34 is connected to thepositive electrode terminal of the power supply 41. A source terminal 3of the third switching device 34 is connected to a drain terminal 6 ofthe fourth switching device 35. A gate terminal 5 of the third switchingdevice 34 and a sense source terminal 4 of the third switching device 34are connected to the third gate drive circuit 38.

A source terminal 3 of the fourth switching device 35 is connected tothe negative electrode terminal of the power supply 41. A gate terminal5 of the fourth switching device 35 and a sense source terminal 4 of thefourth switching device 35 are connected to a fourth gate drive circuit39. A load 42 is connected between a connecting point between the firstswitching device 32 and the second switching device 33 and a connectingpoint between the third switching device 34 and the fourth switchingdevice 35.

The control section 40 comprises a microcomputer including a CPU and amemory (ROM, RAM and the like) storing a program thereof. The controlsection 40 generates a first gate control signal CG1 to a MOSFET 19 ofthe first switching device 32, a second gate control signal CG2 to aMOSFET 19 of the second switching device 33, a third gate control signalCG3 to a MOSFET 19 of the third switching device 34, and a fourth gatecontrol signal CG4 to a MOSFET 19 of the fourth switching device 35, andprovides them to the respective first to fourth gate drive circuits 36to 39.

Based on the respective gate control signals CG1, CG2, CG3, CG4 fed fromthe control section 40, the respective gate drive circuits 36, 37, 38,39 generate gate drive signals DG1, DG2, DG3, DG4 to the first switchingdevice 32, the second switching device 33, the third switching device 34and the fourth switching device 35 and output them. Thus, the first tofourth switching devices 32 to 35 are drive-controlled.

In such an inverter circuit 31, the first switching device 32 and thefourth switching device 35 are turned on, for example. Thereafter, byturning off these switching devices 32 and 35, all of the switchingdevices 32 to 35 are set to a turned-off state. After a predetermineddead time period has passed, the second switching device 33 and thethird switching device 34 are turned on. Thereafter, by turning offthese switching devices 33 and 34, all of the switching devices 32 to 35are set to a turned-off state. After a predetermined dead time periodhas passed, the first switching device 32 and the fourth switchingdevice 35 are again turned on. Repetition of such actions drives theload 42 in AC.

The respective gate drive circuits 36, 37, 38, 39 have an overcurrentprotection function for protecting the corresponding switching devices32, 33, 34, 35 when a short circuit or the like where a voltage of thepower supply 41 is directly applied to these switching devices 32, 33,34, 35 occurs. The case when a short circuit where the voltage of thepower supply 41 is directly applied to the switching devices 32, 33, 34,35 occurs includes, for example, a case where the load 42 isshort-circuited, a case where two switching devices (32, 33; 34, 35)connected in series between the positive electrode terminal and thenegative electrode terminal of the power supply 41 are turned on at thesame time, and a case where one of the two switching devices (32, 33;34, 35) connected in series between the positive electrode terminal andthe negative electrode terminal of the power supply 41 isshort-circuited and damaged. Since configurations of the respective gatedrive circuits 36, 37, 38, 39 are the same, the overcurrent protectionfunction of the first gate drive circuit 36 is described in detailbelow.

FIG. 5 is an electrical circuit diagram showing an electricalconfiguration of the gate drive circuit 36.

The first gate drive circuit 36 includes an amplifier circuit 51, afirst switching circuit 52, a gate resistance 53, a second switchingcircuit 54, a current blocking resistance 55 and an overcurrentdetection circuit 56.

The gate control signal CG1 from the control section 40 is input into aninput terminal of the amplifier circuit 51. The amplifier circuit 51generates the gate drive signal DG1 by amplifying the gate controlsignal CG1. An output terminal of the amplifier circuit 51 is connectedto one input terminal a of the first switching circuit 52. The firstswitching circuit 52 has two input terminals a, b and one outputterminal c, and selects one of the input terminals a, b and connects itto the output terminal c. The other input terminal b of the firstswitching circuit 52 is in an open state. The output terminal c of thefirst switching circuit 52 is connected to the gate terminal 5 of thefirst switching device 32 via the gate resistance 53. The firstswitching circuit 52 is controlled by an output of the overcurrentdetection circuit 56.

The second switching circuit 54 has one input terminal d and two outputterminals e, f, and selects one of the output terminals e, f andconnects to it the input terminal d. The input terminal d is connectedto a connecting point between the gate resistance 53 and the gateterminal 5 of the first switching device 32 via the current blockingresistance 55. The one output terminal e is in an open state. The otheroutput terminal f is grounded. The second switching circuit 54 iscontrolled by an output of the overcurrent detection circuit 56. Aresistance value of the gate resistance 53 is referred to as r1, and aresistance value of the current blocking resistance 55 is referred to asr2. As described below, r2 is set to a value larger than that of r1.

The overcurrent detection circuit 56 includes a current detectingresistance 57 and a comparison circuit 58. One end of the currentdetecting resistance 57 is connected to the sense source terminal 4 ofthe first switching device 32, and the other end of the currentdetecting resistance 57 is grounded. A voltage across the terminals(voltage drop amount) of the current detecting resistance 57 takes avalue according to an amount of a current I_(D) flowing through theMOSFET 19 of the first switching device 32. The voltage across theterminals of the current detecting resistance 57 is fed to thecomparison circuit 58. The comparison circuit 58 determines whether anovercurrent state exists or not by comparing the voltage across theterminals of the current detecting resistance 57 and a referencevoltage, and outputs a determination signal indicative of itsdetermination result. Specifically, the comparison circuit 58 determinesthat the overcurrent state exists when the voltage across the terminalsof the current detecting resistance 57 is larger than the referencevoltage (detects an overcurrent).

In a state where the overcurrent detection circuit 56 does not detectthe overcurrent (normal state), the second switching circuit 54 selectsthe first output terminal e and connects the input terminal d to thefirst output terminal e. Thus, the input terminal d of the secondswitching circuit 54 is set to a high-impedance state. Further, thefirst switching circuit 52 selects the first input terminal a andconnects the first input terminal a to the output terminal c. Thus, thegate drive signal DG1 generated by the amplifier circuit 51 is fed tothe gate terminal 5 of the first switching device 32 via the gateresistance 53. This gate drive signal DG1 drive-controls the MOSFET 19of the first switching device 32.

When the overcurrent detection circuit 56 detects the overcurrent, thefirst switching circuit 52 selects the second input terminal b andconnects the output terminal c to the second input terminal b. Thus, theoutput terminal c of the first switching circuit 52 is set to ahigh-impedance state. Further, the second switching circuit 54 selectsthe second output terminal f and connects the input terminal d to thesecond output terminal f. Thus, the input terminal d of the secondswitching circuit 54 is grounded.

That is, the gate terminal 5 of the first switching device 32 isgrounded via the current blocking resistance 55. As a result of this, agate-to-source voltage Vgs of the first switching device 32 is reduced,and the drain current I_(D) (short-circuit current) flowing in theMOSFET 19 of the first switching device 32 is blocked. A blocking speedof the short-circuit current changes depending on a resistance value r2of the current blocking resistance 55. When the resistance value r2 ofthe current blocking resistance 55 increases, the blocking speed of theshort-circuit current decreases. The resistance value r2 of the currentblocking resistance 55 is larger than a resistance value r1 of the gateresistance 53. In this embodiment, the resistance value r1 of the gateresistance 53 is, for example, 3.9[Ω], and resistance value r2 of thecurrent blocking resistance 55 is, for example, 33[Ω].

While this short-circuit current is blocked by connecting the gateterminal 5 of the first switching device 32 to ground, it takes sometime to blocking. For example, around 10 μsec (microsecond) is requiredfrom detection of an overcurrent. However, if blocking does not occurwithin a short-circuit capacity tsc which the first switching device 32has, thermal destruction of the first switching device 32 may be causedby thermal runaway through the short-circuit current I_(D).

Therefore, in this embodiment, the external resistance 22 having theresistance value r according to the constituent material, length, wirediameter and the like of the source wire 16 (see FIG. 2 ) is connectedin series between the source terminal of the MOSFET 19 and the sensesource terminal 4, as described above.

Thus, in comparison to a case where the sense source terminal 4 isdirectly connected to the source terminal of the MOSFET 19 as in theconventional wire 21 shown in FIG. 5 with a broken line, thegate-to-source voltage Vgs when an overcurrent I_(D) flows between gateand source of the MOSFET 19 can be reduced by a voltage drop (−I_(D)·r)at this external resistance 22.

FIG. 6 is a graph showing a relation between the gate-to-source voltageVgs of the switching device 1 in FIG. 1 and the short-circuit capacitytsc. Specifically, results of a short-circuit test are shown wheresamples of two types of devices having a structure similar to theswitching device 1 in FIG. 1 were produced, one of MOSFETs 19 was formedas DMOS (Double-Diffused MOSFET) and the other of the MOSFETs 19 wasformed as TMOS (Trench MOSFET).

As shown in FIG. 6 , in either of DMOS or TMOS, the short-circuitcapacity tsc increases as the gate-to-source voltage Vgs decreases.Accordingly, as shown in FIG. 5 , if the gate-to-source voltage Vgs whenthe overcurrent I_(D) flows can be reduced by the voltage drop(−I_(D)·r) at the external resistance 22, this can improve ashort-circuit capacity of the first switching device 32. As a result,the short-circuit current I_(D) can be blocked sufficiently in advanceby the grounding of the gate terminal 5.

Moreover, by properly setting a resistance value of the externalresistance 22 through appropriately adjusting the constituent material,length, wire diameter and the like of the source wire 16 (see FIG. 2 ),the voltage drop at the external resistance 22 can be decreased when thedrain current I_(D) flowing between source and drain is relatively smallor is a rated value. For example, in this embodiment, the resistancevalue r of the external resistance 22 is set to I_(D)×1/100 mΩ to5×I_(D)×1/100 mΩ so that the gate-to-source voltage Vgs becomes around18.5 V when the drain current I_(D) is relatively low, thegate-to-source voltage Vgs becomes around 18.0 V when the drain currentI_(D) is the rated value, and the gate-to-source voltage Vgs becomesaround 16.5 V when the drain current I_(D) is four to five times of therated value. Thus, when the drain current I_(D) is relatively small oris the rated value, reduction of the gate-to-source voltage Vgs can besuppressed, and a drive voltage necessary and sufficient for a switchingoperation can be fed to the MOSFET 19. That is, an impact on a switchingperformance of the MOSFET 19 can be small.

Further, in this embodiment, since the source wire 16 for current outputof the switching device 1 is used as the external resistance 22, theeffect of the above-described improvement of the short-circuit capacitycan be achieved with a low cost without the number of componentsincreased.

Further, in this embodiment, since the external resistance 22 is sealedby the resin package 2, the switching device 1 can be installed in aconventional layout.

While one embodiment of the present invention is described above, thepresent invention can be implemented in yet other modes.

For example, in the above-described embodiment, a short-circuit currentis blocked using one current blocking resistance 55, a plurality ofcurrent blocking resistances may be used to change a blocking speed atthe time of current blocking in a stepwise manner.

For example, here is described a case where in FIG. 5 , the gateresistance 53 is used as a first current blocking resistance and thecurrent blocking resistance 55 is used as a second current blockingresistance when an overcurrent is detected. A resistance value r2 of thesecond current blocking resistance (current blocking resistance 55) isset larger than a resistance value r1 of the first current blockingresistance (gate resistance 53). For example, the resistance value r1 is3.9[Ω], and the resistance value r2 is 33[Ω].

In this case, as shown in FIG. 5 by a broken line, the first switchingcircuit 52 has a third input terminal g. The third input terminal g isgrounded. Further, as shown in FIG. 5 by a broken line, the first gatedrive circuit 36 comprises a voltage monitoring portion 59 monitoringthe gate-to-source voltage Vgs of the first switching device 32.

When the overcurrent detection circuit 56 detects an overcurrent, thefirst switching circuit 52 selects the second input terminal b andconnects the output terminal c to the second input terminal b. Thus, theoutput terminal c of the first switching circuit 52 is set to ahigh-impedance state. Further, the second switching circuit 54 selectsthe second output terminal f and connects the input terminal d to thesecond output terminal f. Thus, the input terminal d of the secondswitching circuit 54 is grounded.

That is, the gate terminal 5 of the first switching device 32 isgrounded via the second current blocking resistance 55. As a result, thegate-to-source voltage Vgs of the first switching device 32 is reduced.In this case, since the resistance value of the second current blockingresistance 55 is set larger than the resistance value of the firstcurrent blocking resistance 33, a current blocking speed is slower thanin a case where the gate terminal 5 of the first switching device 32 isgrounded via the first current blocking resistance 53. When thegate-to-source voltage Vgs decreases and takes a voltage value (in thisexample, 10 [V]) where a temperature characteristic of an ON resistanceof the first switching device 32 becomes negative, the voltagemonitoring portion 59 outputs a resistance switching signal to the firstswitching circuit 52 and the second switching circuit 54.

When receiving the resistance switching signal from the voltagemonitoring portion 59, the first switching circuit 52 selects the thirdinput terminal g and connects the output terminal c to the third inputterminal g. When receiving the resistance switching signal from thevoltage monitoring portion 59, the second switching circuit 54 selectsthe first output terminal e and connects the input terminal d to thefirst output terminal e. Thus, the gate terminal 5 of the firstswitching device 32 is grounded via the first current blockingresistance 53 to decrease the gate-to-source voltage Vgs. Since theresistance value of the first current blocking resistance 53 is smallerthan the resistance value of the second current blocking resistance 55,a current blocking speed becomes faster.

Further, in the above-described embodiment, the source wire 16 is usedas the external resistance 22 not to increase the component number.However, an island comprising a metal plate or the like is separatelyprovided in the resin package 2, for example, and the sense sourceterminal 4 and the source pad 13 are connected by at least two wiresusing this island as a relay point.

Further, in the above-described embodiment, the case where the presentinvention is applied to an inverter circuit is described. However, thepresent invention can also be applied to an electronic circuit such as aconverter circuit other than an inverter circuit.

FIGS. 7 to 10 show a semiconductor module to which a switching deviceaccording to one embodiment of the present invention is applied.

FIG. 7 is a plan view for illustrating a configuration of asemiconductor module, and shows a state where a top plate is removed.FIG. 8 is a schematic sectional view along a line VIII-VIII in FIG. 7 .FIG. 9 is a schematic sectional view along a line IX-IX in FIG. 7 .

A semiconductor module 61 includes a heat dissipation plate 62, a casing63, and a plurality of terminals assembled to the casing 63. Theplurality of terminals include a first power-supply terminal (positivepower-supply terminal, in this example) P, a second power-supplyterminal (negative power-supply terminal, in this example) N, as well asa first output terminal OUT1 and a second output terminal OUT2. Further,the plurality of terminals includes a first source sense terminal SS1, afirst gate terminal G1, a second source sense terminal SS2 and a secondgate terminal G2. When the first output terminal OUT1 and the secondoutput terminal OUT2 are collectively referred to, they are referred toas “output terminal OUT”.

For convenience of description, +X direction, −X direction, +Y directionand −Y direction shown in FIG. 7 and +Z direction and −Z direction shownin FIG. 8 are hereinafter sometimes used. The +X direction and the −Xdirection are two directions along a long side of the casing 63 (heatdissipation plate 62) having a generally rectangular shape in a planview, and they are collectively called merely “X direction”. The +Ydirection and the −Y direction are two directions along a short side ofthe casing 63, and they are collectively called merely “Y direction”.The +Z direction and the −Z direction are two directions along a normalline of the casing 63, and they are collectively called merely “Zdirection”. When the heat dissipation plate 62 is placed on a horizontalplane, the X direction and the Y direction are two horizontal directions(first horizontal direction and second horizontal direction) along twohorizontal straight lines (X axis and Y axis) orthogonal to each other,and the Z direction is a vertical direction (height direction) along avertical line (Z axis).

The heat dissipation plate 62 is a plate-shaped body having an elongatedrectangle shape in a plan view and having a uniform thickness, and isformed of a material having a high thermal conductivity. Morespecifically, the heat dissipation plate 62 may be a copper plate formedof copper. This copper plate may be provided with a nickel plating layeron a surface thereof. If necessary, a heat sink or other cooling meansis attached to a surface of the heat dissipation plate 62 on a −Zdirection side.

The casing 63 is formed in a generally rectangular parallelepiped shapeand is formed of a resin material. In particular, a heat resistant resinsuch as PPS (polyphenylene sulfide) is preferably used. The casing 63has a rectangular shape having almost the same size as the heatdissipation plate 62 in a plan view, and comprises a frame portion 64fastened to one surface (surface on a +Z direction side) of the heatdissipation plate 62, and a top plate (not shown) fastened to this frameportion 64. The top plate closes one side (+Z direction side) of theframe portion 64, and is opposed to one surface of the heat dissipationplate 62 closing the other side (−Z direction side) of the frame portion64. Thus, a circuit accommodating space is defined in an inside of thecasing 63 by the heat dissipation plate 62, the frame portion 64 and thetop plate. In this embodiment, the frame portion 64 and theabove-described plurality of terminals are formed by simultaneousmolding.

The frame portion 64 comprises a pair of side walls 66, 67 and a pair ofend walls 68, 69 coupling respective opposite ends of these pair of sidewalls 66, 67. Four corner portions on a surface of the frame portion 64on the +Z direction side are provided with recesses 70 opened outwardly.A wall on an opposite side of an outwardly opened portion of each recess70 curves so as to protrude inwardly. A bottom wall of the recess 70 isprovided with an attachment through hole 71 penetrating the bottom wall.A cylindrical metal member 72 is fastened to the attachment through hole71 in a fitted state. The heat dissipation plate 62 is provided withattachment through holes (not shown) communicating with respectiveattachment through holes 71. The semiconductor module 61 is fastened bya bolt (not shown) inserted through the attachment through holes 71 ofthe casing 63 and the heat dissipation plate 62 to a predeterminedfastening position of an object to be attached. The above-describedcooling means such as a heat sink may be attached using these attachmentthrough holes 71.

An outer surface of the end wall 69 is provided with a terminal board 73for the first power-supply terminal P and a terminal board 74 for thesecond power-supply terminal N. In a plan view, the terminal board 73 isdisposed on a +Y direction side with respect to a length directioncenter of the end wall 69, and the terminal board 74 is disposed on a −Ydirection side with respect to the length direction center of the endwall 69. These terminal boards 73 and 74 are integrally formed with theend wall 69.

An outer surface of the end wall 68 is provided with a terminal board 75for the first output terminals OUT1 and a terminal board 76 for thesecond output terminals OUT2. In a plan view, the terminal board 75 isdisposed on the +Y direction side with respect to a length directioncenter of the end wall 68, and the terminal board 76 is disposed on the−Y direction side with respect to the length direction center of the endwall 68. These terminal boards 75 and 76 are integrally formed with theend wall 68. Nuts (not shown) are respectively embedded in therespective terminal boards 73, 74, 75, 76 in positions where center axislines of screw holes of the respective nuts correspond to the Zdirection.

The first power-supply terminal P is disposed on a surface (surface onthe +Z direction side) of the terminal board 73. The second power-supplyterminal N is disposed on a surface (surface on the +Z direction side)of the terminal board 74. The first output terminal OUT1 is disposed ona surface (surface on the +Z direction side) of the terminal board 75.The second output terminal OUT2 is disposed on a surface (surface on the+Z direction side) of the terminal board 76.

Each of the first power-supply terminal P, the second power-supplyterminal N, the first output terminal OUT1 and the second outputterminal OUT2 is formed by cutting out a metal plate (for example, acopper plate provided with a nickel plating) into a predetermined shapeto be subjected to bending, and is electrically connected to a circuitin the inside of the casing 63. Respective tip portions of the firstpower-supply terminal P, the second power-supply terminal N, the firstoutput terminal OUT1 and the second output terminal OUT2 are drawn outon the terminal boards 73, 74, 75, 76. The respective tip portions ofthe first power-supply terminal P, the second power-supply terminal N,the first output terminal OUT1 and the second output terminal OUT2 areformed so as to be along respective surfaces of the terminal boards 73,74, 75, 76. The tip portions of the first power-supply terminal P, thesecond power-supply terminal N, the first output terminal OUT1 and thesecond output terminal OUT2 are respectively provided with through holes83 d, 84 d, 85 d, 86 d. The terminals P, N, OUT1, OUT2 can be connectedto bus bars provided on a side of the object to be attached to thesemiconductor module 61 by being inserted through these through holes 83d, 84 d, 85 d, 86 d and using bolts threaded into the above-describednuts.

The first source sense terminal SS1, the first gate terminal G1 and thelike are attached to the one side wall 67. Tip portions of theseterminals SS1, G1 protrude from a surface (surface on the +Z directionside) of the side wall 67 outwardly (in the +Z direction) of the casing63. The first source sense terminal SS1 and the first gate terminal G1are disposed between an end on a −X direction side and a lengthdirection (X direction) center of the side wall 67 in a manner spaced inthe X direction.

The second gate terminal G2 and the second source sense terminal SS2 areattached to the other side wall 66. Tip portions of these terminals G2,SS2 protrude from a surface (surface on the +Z direction side) of theside wall 66 outwardly (in the +Z direction) of the casing 63. Thesecond gate terminal G2 and the second source sense terminal SS2 aredisposed between a length direction (X direction) center and an end onthe +X direction side of the side wall 66 in a manner spaced in the Xdirection. Each of the source sense terminals SS1, SS2 and gateterminals G1, G2 is formed by subjecting a metal rod (for example, acopper rod-like body provided with a nickel plating) having arectangular cross-section to bending, and is electrically connected tothe circuit in the inside of the casing 63.

The first power-supply terminal P includes a tip portion 83 a along thesurface of the terminal board 73, a base portion 83 b disposedparallelly to the tip portion 83 a on the −Z direction side with respectto the tip portion 83 a, and a standing portion coupling the tip portion83 a and the base portion 83 b. The standing portion couples an edgeportion of the base portion 83 b on the −Y direction side and an edgeportion of the base portion 83 a on the −Y direction side. Most of thebase portion 83 b and the standing portion of the first power-supplyterminal P are embedded in insides of the end wall 69 and the terminalboard 73. A comb-shaped terminal 83 c protruding inwardly of the casing63 is formed on an end portion of the base portion 83 b on the −Xdirection side.

The second power-supply terminal N includes a tip portion 84 a along thesurface of the terminal board 74, a base portion 84 b disposedparallelly to the tip portion 84 a on the −Z direction side with respectto the tip portion 84 a, and a standing portion coupling the tip portion84 a and the base portion 84 b. The standing portion couples an edgeportion of the base portion 84 b on the +Y direction side and an edgeportion of the base portion 84 a on the +Y direction. Most of the baseportion 84 b and the standing portion of the second power-supplyterminal N are embedded in insides of the end wall 69 and the terminalboard 74. A comb-shaped terminal 84 c protruding inwardly of the casing63 is formed on an end portion of the base portion 84 b on the −Xdirection side.

The first output terminal OUT1 includes a tip portion 85 a along thesurface of the terminal board 75, a base portion 85 b disposedparallelly to the tip portion 85 a on the −Z direction side with respectto the tip portion 85 a, and a standing portion coupling the tip portion85 a and the base portion 85 b. The standing portion couples an edgeportion of the base portion 85 b on the −Y direction side and an edgeportion of the base portion 85 a on the −Y direction side. Most of thebase portion 85 b and the standing portion of the first output terminalOUT1 are embedded in insides of the end wall 68 and the terminal board75. A comb-shaped terminal 85 c protruding inwardly of the casing 63 isformed on an end portion of the base portion 85 b on the +X directionside.

The second output terminal OUT2 includes a tip portion 86 a along thesurface of the terminal board 76, a base portion 86 b disposedparallelly to the tip portion 86 a on the −Z direction side with respectto the tip portion 86 a, and a standing portion coupling the tip portion86 a and the base portion 86 b. The standing portion couples an edgeportion of the base portion 86 b on the +Y direction side and an edgeportion of the base portion 86 a on the +Y direction side. Most of thebase portion 86 b and the standing portion of the second output terminalOUT2 are embedded in insides of the end wall 68 and the terminal board76. A comb-shaped terminal 86 c protruding inwardly of the casing 63 isformed on an end portion of the base portion 86 b on the +X directionside.

The first source sense terminal SS1 has a crank shape viewed from the Xdirection, and their intermediate portion is embedded in the side wall67. A base end portion of the first source sense terminal SS1 isdisposed in the casing 63. A tip end portion of the first source senseterminal SS1 protrudes from the surface of the side wall 67 in the +Zdirection.

The first gate terminal G1 has a crank shape viewed from the Xdirection, and their intermediate portion is embedded in the side wall67. A base end portion of the first gate terminal G1 is disposed in thecasing 63. A tip end portion of the first gate terminal G1 protrudesfrom the surface of the side wall 67 in the +Z direction.

The second source sense terminal SS2 has a crank shape viewed from the Xdirection, and their intermediate portion is embedded in the side wall66. A base end portion of the second source sense terminal SS2 isdisposed in the casing 63. A tip end portion of the second source senseterminal SS2 protrudes from the surface of the side wall 66 in the +Zdirection.

The second gate terminal G2 has a crank shape viewed from the Xdirection, and their intermediate portion is embedded in the side wall66. A base end portion of the second gate terminal G2 is disposed in thecasing 63. A tip end portion of the second gate terminal G2 protrudesfrom the surface of the side wall 66 in the +Z direction.

In a region surrounded by the frame portion 64 in the surface (surfaceon the +Z direction side) of the heat dissipation plate 62, a firstassembly 100 and a second assembly 200 are disposed side by side in theX direction. The first assembly 100 is disposed on a side of thepower-supply terminals P, N, and the second assembly 200 is disposed ona side of the output terminal OUT. The first assembly 100 configures ahalf of an upper arm (high side) circuit and a half of a lower arm (lowside) circuit. The second assembly 200 configures the other half of theupper arm circuit and the other half of the lower arm circuit.

The first assembly 100 includes a first insulating substrate 101, aplurality of first switching elements Tr1, a plurality of first diodeelements Di1, a plurality of second switching elements Tr2 and aplurality of second diode elements Di2.

The first insulating substrate 101 has a generally rectangular shape ina plan view, and four sides thereof are joined to the surface of theheat dissipation plate 62 in positions where the four sides respectivelyparallel to four sides of the heat dissipation plate 62. A surface(surface on the −Z direction side) of the first insulating substrate 101on a side of the heat dissipation plate 62 is provided with a firstjoining conductor layer 102 (see FIG. 8 ). This first joining conductorlayer 102 is joined to the heat dissipation plate 62 via a solder layer131.

An surface (surface on the +Z direction side) of the first insulatingsubstrate 101 on a side opposite to the heat dissipation plate 62 isprovided with a plurality of conductor layers for the upper arm circuitand a plurality of conductor layers for the lower arm circuit. Theplurality of conductor layers for the upper arm circuit includes a firstelement joining conductor layer 103, a first gate terminal conductorlayer 104 and a first source-sense-terminal conductor layer 105. Theplurality of conductor layers for the lower arm circuit includes asecond element joining conductor layer 106, an N-terminal conductorlayer 107, a second gate terminal conductor layer 108 and a secondsource-sense-terminal conductor layer 109.

In this embodiment, the first insulating substrate 101 is formed of AIN.For example, a substrate where copper foils are directly joined toopposite surfaces of ceramics (DBC: Direct Bonding Copper) can be usedas the first insulating substrate 101. When a DBC substrate is used asthe first insulating substrate 101, the respective conductor layers 102to 109 are formed by the copper foils.

The first element joining conductor layer 103 is disposed near a side onthe +Y direction side on a surface of the first insulating substrate101, and has a rectangular shape elongated in the X direction in a planview. The first element joining conductor layer 103 has on an endportion thereof on the +X direction side a protruding portion extendingin the −Y direction. The N-terminal conductor layer 107 is disposed neara side on the −Y direction side on the surface of the first insulatingsubstrate 101, and has a rectangular shape elongated in the X directionin a plan view. The N-terminal conductor layer 107 has on an end portionthereof on the +X direction side a protruding portion extending towardthe protruding portion of the first element joining conductor layer 103.The second element joining conductor layer 106 is disposed on a regionsurrounded by the first element joining conductor layer 103, theN-terminal conductor layer 107 and a side of the first insulatingsubstrate 101 on the −X direction side in a plan view, and has arectangular shape elongated in the X direction in a plan view.

The first gate terminal conductor layer 104 is disposed between thefirst element joining conductor layer 103 and the side of the firstinsulating substrate 101 on the +Y direction side, and has a rectangularshape elongated in the X direction in a plan view. The firstsource-sense-terminal conductor layer 105 is disposed between the firstgate terminal conductor layer 104 and the side of the first insulatingsubstrate 101 on the +Y direction side, and has a rectangular shapeelongated in the X direction in a plan view.

The second gate terminal conductor layer 108 is disposed between theN-terminal conductor layer 107 and the side of the first insulatingsubstrate 101 on the −Y direction side, and has a rectangular shapeelongated in the X direction in a plan view. The secondsource-sense-terminal conductor layer 109 is disposed between the secondgate terminal conductor layer 108 and the side of the first insulatingsubstrate 101 on the −Y direction side, and has a rectangular shapeelongated in the X direction in a plan view.

The comb-shaped terminal 83 c of the first power-supply terminal P isjoined to an end portion on the +X direction side on a surface of thefirst element joining conductor layer 103. The comb-shaped terminal 84 cof the second power-supply terminal N is joined to an end portion on the+X direction side on a surface of the N-terminal conductor layer 107. Aterminal of the first power-supply terminal P has a comb shape like thecomb-shaped terminal 83 c. Therefore, when the first power-supplyterminal P is joined to the first element joining conductor layer 103,the comb-shaped terminal 83 c can easily be ultrasonically joined to thefirst element joining conductor layer 103 by pressing a head forultrasonic joining against a tip of the comb-shaped terminal 83 c, forexample. Further, a terminal of the second power-supply terminal N has acomb shape like the comb-shaped terminal 84 c. Therefore, when thesecond power-supply terminal N is joined to the N-terminal conductorlayer 107, the comb-shaped terminal 84 c can easily be ultrasonicallyjoined to the N-terminal conductor layer 107 by pressing a head forultrasonic joining against a tip of the comb-shaped terminal 84 c, forexample. The base end portion of the second gate terminal G2 is joinedto the second gate terminal conductor layer 108. The base end portion ofthe second source sense terminal SS2 is joined to the secondsource-sense-terminal conductor layer 109. Joining of them may beperformed by ultrasonic joining.

To the surface of the first element joining conductor layer 103, drainelectrodes of the plurality of first switching elements Tr1 are joinedvia a solder layer 132 (see FIG. 8 ), and at the same time, cathodeelectrodes of the plurality of first diode elements Di1 are joined via asolder layer 133. Each first switching element Tr1 has a sourceelectrode and a gate electrode on a surface opposite to a surface joinedto the first element joining conductor layer 103. Each first diodeelement Di1 has an anode electrode on a surface opposite to a surfacejoined to the first element joining conductor layer 103.

Near a side on the +Y direction side on the surface of the first elementjoining conductor layer 103, five first diode elements Di1 are disposedside by side in a manner spaced in the X direction. Further, between aside of a first element joining conductor layer 103 on the −Y directionside and the five first diode elements Di1, five first switchingelements Tr1 are disposed side by side in a manner spaced in the Xdirection. The five first switching elements Tr1 are aligned with thefive first diode elements Di1 with respect to the Y direction.

The first switching element Tr1 and the first diode element Di1 alignedin the Y direction are connected to the second element joining conductorlayer 106 by a first connection metal member 110 extending generally inthe Y direction in a plan view. The first connection metal member 110comprises a block-shaped standing portion whose base end portion isjoined to the second element joining conductor layer 106 via a solder134 and whose tip end portion extends in the +Z direction, and aplate-shaped traverse portion extending from the tip end portion of thestanding portion in the +Y direction and disposed above the firstswitching element Tr1 and the first diode element Di1. A tip end portionof the traverse portion is joined to the anode electrode of the firstdiode element Di1 via a solder 135, and a length intermediate portion ofthe traverse portion is joined to the source electrode of the firstswitching element Tr1 via a solder 136. A width (length in the Xdirection) of the first connection metal member 110 is shorter than awidth (length in the X direction) of the first switching element Tr1.The traverse portion of the first connection metal member 110 passes anintermediate portion of the width of the first switching element Tr1 ina plan view.

The gate electrode of each first switching element Tr1 is connected tothe first gate terminal conductor layer 104 via a wire 111. Each firstconnection metal member 110 is connected to the firstsource-sense-terminal conductor layer 105 via a wire 112. That is, thesource electrode of each first switching element Tr1 is connected to thefirst source-sense-terminal conductor layer 105 via the solder 136, thefirst connection metal member 110 and the wire 112.

To the surface of the second element joining conductor layer 106, drainelectrodes of the plurality of second switching elements Tr2 areconnected via a solder layer 137 (see FIG. 8 ), and at the same time,cathode electrodes of the plurality of second diode elements Di2 areconnected via a solder layer 138. Each second switching element Tr2 hasa source electrode and a gate electrode on a surface opposite to asurface joined to the second element joining conductor layer 106. Eachsecond diode element Di2 has an anode electrode on a surface opposite toa surface joined to the second element joining conductor layer 106.

Near a side on the −Y direction side on the surface of the secondelement joining conductor layer 106, five second switching elements Tr2are disposed side by side in a manner spaced in the X direction.Further, between a side of the second element joining conductor layer106 on the +Y direction side and the five second switching elements Tr2,five second diode elements Di2 are disposed side by side in a mannerspaced in the X direction. The five second diode elements Di2 arealigned with the five second switching elements Tr2 with respect to theY direction. Further, the five second diode elements Di2 are alsoaligned with the five first switching elements Tr1 with respect to the Ydirection.

The second switching element Tr2 and the second diode element Di2aligned in the Y direction are connected to the N-terminal conductorlayer 107 by a second connection metal member 120 extending generally inthe Y direction in a plan view. The second connection metal member 120comprises a block-shaped standing portion whose base end portion isjoined to the N-terminal conductor layer 107 via a solder 139 and whosetip end portion extends in the +Z direction, and a plate-shaped traverseportion extending from the tip end portion of the standing portion inthe +Y direction and disposed above the second switching element Tr2 andthe second diode element Di2. A tip end portion of the traverse portionis joined to the anode electrode of the second diode element Di2 via asolder 140, and a length intermediate portion of the traverse portion isjoined to the source electrode of the second switching element Tr2 via asolder 141. A width (length in the X direction) of the second connectionmetal member 120 is shorter than a width (length in the X direction) ofthe second switching element Tr2. The traverse portion of the secondconnection metal member 120 passes an intermediate portion of the widthof the second switching element Tr2 in a plan view.

The gate electrode of each second switching element Tr2 is connected tothe second gate terminal conductor layer 108 via a wire 121. TheN-terminal conductor layer 107 is connected to the secondsource-sense-terminal conductor layer 109 via a wire 122. That is, thesource electrode of each second switching element Tr2 is connected tothe second source-sense-terminal conductor layer 109 via the solder 141,the second connection metal member 120, the N-terminal conductor layer107 and the wire 122.

The second assembly 200 includes a second insulating substrate 201, aplurality of third switching elements Tr3, a plurality of third diodeelements Di3, a plurality of fourth switching elements Tr4 and aplurality of fourth diode elements Di4.

The second insulating substrate 201 has a generally rectangular shape ina plan view, and four sides thereof are joined to the surface of theheat dissipation plate 62 in positions where the four sides respectivelyparallel to four sides of the heat dissipation plate 62. A surface(surface on the −Z direction side) of the second insulating substrate201 on the side of the heat dissipation plate 62 is provided with asecond joining conductor layer 202 (see FIG. 9 ). This second joiningconductor layer is joined to the heat dissipation plate 62 via a solderlayer 231.

An surface (surface on the +Z direction side) of the second insulatingsubstrate 201 on a side opposite to the heat dissipation plate 62 isprovided with a plurality of conductor layers for the upper arm circuitand a plurality of conductor layers for the lower arm circuit. Theplurality of conductor layers for the upper arm circuit include a thirdelement joining conductor layer 203, a third gate terminal conductorlayer 204 and a third source-sense-terminal conductor layer 205. Theplurality of conductor layers for the lower arm circuit include a fourthelement joining conductor layer 206, an source conductor layer 207, afourth gate terminal conductor layer 208 and a fourthsource-sense-terminal conductor layer 209.

In this embodiment, the second insulating substrate 201 is formed ofAIN. For example, a substrate where copper foils are directly joined toopposite surfaces of ceramics (DBC: Direct Bonding Copper) can be usedas the second insulating substrate 201. When a DBC substrate is used asthe second insulating substrate 201, the respective conductor layers 202to 209 are formed by the copper foils.

The third element joining conductor layer 203 is disposed near a side onthe +Y direction side on a surface of the second insulating substrate201, and has a rectangular shape elongated in the X direction in a planview. The third element joining conductor layer 203 has on an endportion thereof on the −X direction side a protruding portion extendingin the +Y direction. The source conductor layer 207 is disposed near aside on the −Y direction side on the surface of the second insulatingsubstrate 201, and has a rectangular shape elongated in the X directionin a plan view. The fourth element joining conductor layer 206 has a Tshape in a plan view, is disposed between the third element joiningconductor layer 203 and the source conductor layer 207, and includes anelement joining portion 206 a having a rectangular shape elongated inthe X direction in a plan view and an output terminal joining portion206 b extending along a side of the second insulating substrate 201 onthe −X direction side. An end portion of the element joining portion 206a on the −X direction side is coupled to a length center portion of theoutput terminal joining portion 206 b.

The third gate terminal conductor layer 204 is disposed between thethird element joining conductor layer 203 and a side of the secondinsulating substrate 201 on the +Y direction side, and has a rectangularshape elongated in the X direction in a plan view. The thirdsource-sense-terminal conductor layer 205 is disposed between the thirdgate terminal conductor layer 204 and the side of the second insulatingsubstrate 201 on the +Y direction side, and has a rectangular shapeelongated in the X direction in a plan view.

The fourth gate terminal conductor layer 208 is disposed between thesource conductor layer 207 and the side of the second insulatingsubstrate 201 on the −Y direction side, and has a rectangular shapeelongated in the X direction in a plan view. The fourthsource-sense-terminal conductor layer 209 is disposed between the fourthgate terminal conductor layer 208 and the side of the second insulatingsubstrate 201 on the −Y direction side, and has a rectangular shapeelongated in the X direction in a plan view.

The comb-shaped terminal 85 c of the first output terminal OUT1 and thecomb-shaped terminal 86 c of the second output terminal OUT2 are joinedto a surface of the output terminal joining portion 206 b of the fourthelement joining conductor layer 206. A terminal of the first outputterminal OUT1 has a comb shape like the comb-shaped terminal 85 c.Therefore, when the first output terminal OUT1 is joined to the outputterminal joining portion 206 b, the comb-shaped terminal 85 c can easilybe ultrasonically joined to the output terminal joining portion 206 b bypressing a head for ultrasonic joining against a tip of the comb-shapedterminal 85 c, for example. Further, a terminal of the second outputterminal OUT2 has a comb shape like the comb-shaped terminal 86 c.Therefore, when the second output terminal OUT2 is joined to the outputterminal joining portion 206 b, the comb-shaped terminal 86 c can easilybe ultrasonically joined to the output terminal joining portion 206 b bypressing a head for ultrasonic joining against a tip of the comb-shapedterminal 86 c, for example. The base end portion of the first gateterminal G1 is joined to the third gate terminal conductor layer 204.The base end portion of the first source sense terminal SS1 is joined tothe third source-sense-terminal conductor layer 205. Joining of them maybe performed by ultrasonic joining.

To a surface of the third element joining conductor layer 203, drainelectrodes of the plurality of third switching elements Tr3 are joinedvia a solder layer 232 (see FIG. 9 ), and at the same time, cathodeelectrodes of the plurality of third diode elements Di3 are joined via asolder layer 233. Each third switching element Tr3 has a sourceelectrode and a gate electrode on a surface opposite to a surface joinedto the third element joining conductor layer 203. Each third diodeelement Di3 has an anode electrode on a surface opposite to a surfacejoined to the third element joining conductor layer 203.

Near a side on the +Y direction side on the surface of the third elementjoining conductor layer 203, five third diode elements Di3 are disposedside by side in a manner spaced in the X direction. Further, between aside of the third element joining conductor layer 203 on the −Ydirection side and the five third diode elements Di3, five thirdswitching elements Tr3 are disposed side by side in a manner spaced inthe X direction. The five third switching elements Tr3 are aligned withthe five third diode elements Di3 with respect to the Y direction.

The third switching element Tr3 and the third diode element Di3 alignedin the Y direction are connected to the fourth element joining conductorlayer 206 by a third connection metal member 210 extending generally inthe Y direction in a plan view. The third connection metal member 210comprises a block-shaped standing portion whose base end portion isjoined to the fourth element joining conductor layer 206 via a solder234 and whose tip end portion extends in the +Z direction, and aplate-shaped traverse portion extending from the tip end portion of thestanding portion in the +Y direction and disposed above the thirdswitching element Tr3 and the third diode element Di3. A tip end portionof the traverse portion is joined to the anode electrode of the thirddiode element Di3 via a solder 235, and a length intermediate portion ofthe traverse portion is joined to the source electrode of the thirdswitching element Tr3 via a solder 236. A width (length in the Xdirection) of the third connection metal member 210 is shorter than awidth (length in the X direction) of the third switching element Tr3.The traverse portion of the third connection metal member 210 passes anintermediate portion of the width of the third switching element Tr3 ina plan view.

The gate electrode of each third switching element Tr3 is connected tothe third gate terminal conductor layer 204 via a wire 211. Each thirdconnection metal member 210 is connected to the thirdsource-sense-terminal conductor layer 205 via a wire 212. That is, thesource electrode of each third switching element Tr3 is connected to thethird source-sense-terminal conductor layer 205 via the solder 236, thethird connection metal member 210 and the wire 212.

To the surface of the fourth element joining conductor layer 206, drainelectrodes of the plurality of fourth switching elements Tr4 areconnected via a solder layer 237 (see FIG. 9 ), and at the same time,cathode electrodes of the plurality of fourth diode elements Di4 areconnected via a solder layer 238. Each fourth switching element Tr4 hasa source electrode and a gate electrode on a surface opposite to asurface joined to the fourth element joining conductor layer 206. Eachfourth diode element Di4 has an anode electrode on a surface opposite toa surface joined to the fourth element joining conductor layer 206.

Near a side on the −Y direction side on the surface of the fourthelement joining conductor layer 206, five fourth switching elements Tr4are disposed side by side in a manner spaced in the X direction.Further, between a side of the fourth element joining conductor layer206 on the +Y direction side and the five fourth switching elements Tr4,five fourth diode elements Di4 are disposed side by side in a mannerspaced in the X direction. The five fourth diode elements Di4 arealigned with the five fourth switching elements Tr4 with respect to theY direction. Further, the five fourth diode elements Di4 are alsoaligned with the five third switching elements Tr3 with respect to the Ydirection.

The fourth switching element Tr4 and the fourth diode element Di4aligned in the Y direction are connected to the source conductor layer207 by a fourth connection metal member 220 extending generally in the Ydirection in a plan view. The fourth connection metal member 220comprises a block-shaped standing portion whose base end portion isjoined to the source conductor layer 207 via a solder 239 and whose tipend portion extends in the +Z direction, and a plate-shaped traverseportion extending from the tip end portion of the standing portion anddisposed above the fourth switching element Tr4 and the fourth diodeelement Di4. The tip end portion of the traverse portion is joined tothe anode electrode of the fourth diode element Di4 via a solder 240,and a length intermediate portion of the traverse portion is joined tothe source electrode of the fourth switching element Tr4 via a solder241. A width (length in the X direction) of the fourth connection metalmember 220 is shorter than a width (length in the X direction) of thefourth switching element Tr4. The traverse portion of the fourthconnection metal member 220 passes an intermediate portion of the widthof the fourth switching element Tr4 in a plan view.

The gate electrode of each fourth switching element Tr4 is connected tothe fourth gate terminal conductor layer 208 via a wire 221.

The third element joining conductor layer 203 of the second assembly 200is connected to the first element joining conductor layer 103 of thefirst assembly 100 by a first conductor layer connecting member 91. Thefirst conductor layer connecting member 91 comprises a plate-shaped bodyhaving an H shape in a plan view, and is formed of a pair of rectangularportions across the third element joining conductor layer 203 and thefirst element joining conductor layer 103 as well as a linking portionlinking center portions of these rectangular portions. Since the firstelement joining conductor layer 103 and the third element joiningconductor layer 203 are connected by the first conductor layerconnecting member 91, reduction in inductance can be planned to achievein comparison to a case of connecting by a wire, for example. Further,the first conductor layer connecting member 91 has the H shape in a planview, and a terminal of the first conductor layer connecting member 91has a comb shape. Therefore, when the first conductor layer connectingmember 91 is joined to the first element joining conductor layer 103,for example, the first conductor layer connecting member 91 can easilybe ultrasonically joined to the first element joining conductor layer103 by pressing a head for ultrasonic joining against a tip of the firstconductor layer connecting member 91.

The fourth element joining conductor layer 206 of the second assembly200 is connected to the second element joining conductor layer 106 ofthe first assembly 100 by a second conductor layer connecting member 92.The second conductor layer connecting member 92 comprises a plate-shapedbody having an H shape in a plan view, and is formed of a pair ofrectangular portions across the fourth element joining conductor layer206 and the second element joining conductor layer 106 as well as alinking portion linking center portions of these rectangular portions.Since the second element joining conductor layer 106 and the fourthelement joining conductor layer 206 are connected by the secondconductor layer connecting member 92, reduction in inductance can beplanned to achieve in comparison to a case of connecting by a wire, forexample. Further, the second conductor layer connecting member 92 hasthe H shape in a plan view, and a terminal of the second conductor layerconnecting member 92 has a comb shape. Therefore, when the secondconductor layer connecting member 92 is joined to the second elementjoining conductor layer 106, for example, the second conductor layerconnecting member 92 can easily be ultrasonically joined to the secondelement joining conductor layer 106 by pressing a head for ultrasonicjoining against a tip of the second conductor layer connecting member92.

The source conductor layer 207 of the second assembly 200 is connectedto the N-terminal conductor layer 107 of the first assembly 100 by athird conductor layer connecting member 93. The third conductor layerconnecting member 93 comprises a plate-shaped body having an H shape ina plan view, and is formed of a pair of rectangular portions across thesource conductor layer 207 and the N-terminal conductor layer 107 aswell as a linking portion linking center portions of these rectangularportions. Since the N-terminal conductor layer 107 and the sourceconductor layer 207 are connected by the third conductor layerconnecting member 93, reduction in inductance can be planned to achievein comparison to a case of connecting by a wire, for example. Further,the third conductor layer connecting member 93 has the H shape in a planview, and a terminal of the third conductor layer connecting member 93has a comb shape. Therefore, when the third conductor layer connectingmember 93 is joined to the N-terminal conductor layer 107, for example,the third conductor layer connecting member 93 can easily beultrasonically joined to the N-terminal conductor layer 107 by pressinga head for ultrasonic joining against a tip of the third conductor layerconnecting member 93.

The third gate terminal conductor layer 204 of the second assembly 200is connected to the first gate terminal conductor layer 104 of the firstassembly 100 via a wire 94. The third source-sense-terminal conductorlayer 205 of the second assembly 200 is connected to the firstsource-sense-terminal conductor layer 105 of the first assembly 100 viaa wire 95.

The fourth gate terminal conductor layer 208 of the second assembly 200is connected to the second gate terminal conductor layer 108 of thefirst assembly 100 via a wire 96.

FIG. 10 is an electrical circuit diagram showing an electricalconfiguration of the semiconductor module 61. FIG. 10 shows the twooutput terminals OUT1, OUT2 as one output terminal OUT.

The plurality of first switching elements Tr1 and the plurality of firstdiode elements Di1 provided on the first assembly 100 as well as theplurality of third switching elements Tr3 and the plurality of thirddiode elements Di3 provided on the second assembly 200 are parallellyconnected between the first power-supply terminal P and the outputterminal OUT to form an upper arm circuit (high side circuit) 301. Theplurality of second switching elements Tr2 and the plurality of seconddiode elements Di2 provided on the first assembly 100 as well as theplurality of fourth switching elements Tr4 and the plurality of fourthdiode elements Di4 provided on the second assembly 200 are connectedbetween the output terminal OUT and the second power-supply terminal Nto form a lower arm circuit (low side circuit) 302.

The upper arm circuit 301 and the lower arm circuit 302 are connected inseries between the first power-supply terminal P and the secondpower-supply terminal N, and the output terminal OUT is connected to aconnecting point 303 between the upper arm circuit 301 and the lower armcircuit 302. Thus, a half bridge circuit is configured. This half bridgecircuit can be used as a single-phase bridge circuit. Further, amulti-phase (for example, three-phase) bridge circuit can be configuredby parallelly connecting a plurality (for example, three) of the halfbridge circuits (semiconductor module 1) to the power source.

In this embodiment, the first to fourth switching elements Tr1 to Tr4are configured of N-channel DMOS (Double-Diffused Metal OxideSemiconductor) field effect transistors. In particular, in thisembodiment, the first to fourth switching elements Tr1 to Tr4 arehigh-speed switching MOSFETs formed of SiC semiconductor devices(SiC-DMOS).

Further, in this embodiment, the first to fourth diode elements Di1 toDi4 are configured of schottky barrier diodes (SBD). In particular, inthis embodiment, the first to fourth diode elements Di1 to Di4 areconfigured of SiC semiconductor devices (SiC-SBD).

The first diode element Di1 is parallelly connected to each firstswitching element Tr1. The third diode element Di3 is parallellyconnected to each third switching element Tr3. The respective drains ofeach first switching element Tr1 and each third switching element Tr3 aswell as the respective cathodes of each first diode element Di1 and eachthird diode element Di3 are connected to the first power-supply terminalP.

The anodes of the plurality of first diode elements Di1 are connected tothe sources of the corresponding first switching elements Tr1, and thesources of the first switching elements Tr1 are connected to the outputterminal OUT. Similarly, the anodes of the plurality of third diodeelements Di3 are connected to the sources of the corresponding thirdswitching elements Tr3, and the sources of the third switching elementsTr3 are connected to the output terminal OUT.

The gates of the plurality of first diode elements Di1 and the pluralityof third diode elements Di3 are connected to the first gate terminal G1.The sources of the plurality of first switching elements Tr1 and thethird switching elements Tr3 are also connected to the first sourcesense terminal SS1.

The source of the first switching element Tr1 is connected to the firstsource sense terminal SS1 via the solder 136, the first connection metalmember 110, the wire 112, the first source-sense-terminal conductorlayer 105, the wire 95 and the third source-sense-terminal conductorlayer 205. Therefore, there exists between the source of the firstswitching element Tr1 and the first source sense terminal SS1 a wiringresistance including a resistance (external resistance) R1 parasiting ina current path formed of the solder 136 and the first connection metalmember 110. In this embodiment, the wiring resistance between the sourceof the first switching element Tr1 and the first source sense terminalSS1 is larger by an amount of the external resistance R1 in comparisonto a case of directly connecting one end of the wire 112 to the sourceof the first switching element Tr1.

Further, the source of the third switching element Tr3 is connected tothe first source sense terminal SS1 via the solder 236, the thirdconnection metal member 210, the wire 212 and the thirdsource-sense-terminal conductor layer 205. Therefore, there existsbetween the source of the third switching element Tr3 and the firstsource sense terminal SS1 a wiring resistance including a resistance(external resistance) R3 parasiting in a current path formed of thesolder 236 and the third connection metal member 210. In thisembodiment, the wiring resistance between the source of the thirdswitching element Tr3 and the first source sense terminal SS1 is largerby an amount of the external resistance R3 in comparison to a case ofdirectly connecting one end of the wire 212 to the source of the thirdswitching element Tr3.

The second diode element Di2 is parallelly connected to each secondswitching element Tr2. The fourth diode element Di4 is parallellyconnected to each fourth switching element Tr4. The respective drains ofeach second switching element Tr2 and each fourth switching element Tr4as well as the respective cathodes of each second diode element Di2 andeach fourth diode element Di4 are connected to the output terminal OUT.

The anodes of the plurality of second diode elements Di2 are connectedto the sources of the corresponding second switching elements Tr2, andthe sources of the second switching elements Tr2 are connected to thesecond power-supply terminal N. Similarly, the anodes of the pluralityof fourth diode elements Di4 are connected to the sources of thecorresponding fourth switching elements Tr4, and the sources of thefourth switching elements Tr4 are connected to the second power-supplyterminal N.

The gates of the plurality of second diode elements Di2 and theplurality of fourth diode elements Di4 are connected to the second gateterminal G2. The sources of the plurality of second switching elementsTr2 and the fourth switching elements Tr4 are also connected to thesecond source sense terminal SS2.

The source of the second switching element Tr2 is connected to thesecond source sense terminal SS2 via the solder 141, the secondconnection metal member 120, the N-terminal conductor layer 107, thewire 122 and the second source-sense-terminal conductor layer 109.Therefore, there exists between the source of the second switchingelement Tr2 and the second source sense terminal SS2 a wiring resistanceincluding a resistance (external resistance) R2 parasiting in a currentpath formed of the solder 141, the second connection metal member 120and the N-terminal conductor layer 107. In this embodiment, the wiringresistance between the source of the second switching element Tr2 andthe second source sense terminal SS2 is larger by an amount of theexternal resistance R2 in comparison to a case of directly connectingone end of the wire 212 to the source of the second switching elementTr2.

Further, the source of the fourth switching element Tr4 is connected tothe second source sense terminal SS2 via the solder 241, the fourthconnection metal member 220, the source conductor layer 207, the thirdconductor layer connecting member 93, the N-terminal conductor layer107, the wire 122 and the second source-sense-terminal conductor layer109. Therefore, there exists between the source of the fourth switchingelement Tr4 and the second source sense terminal SS2 a wiring resistanceincluding a resistance (external resistance) R4 parasiting in a currentpath formed of the solder 241, the fourth connection metal member 220,the third conductor layer connecting member 93 and the N-terminalconductor layer 107. In this embodiment, the wiring resistance betweenthe source of the fourth switching element Tr4 and the second sourcesense terminal SS2 is larger by an amount of the external resistance R4in comparison to a case of directly connecting the source of the fourthswitching element Tr4 and the second source-sense-terminal conductorlayer 109 by a wire.

In place of connecting the N-terminal conductor layer 107 to the secondsource-sense-terminal conductor layer 109 by the wire 122, each secondconnection metal member 120 may be connected to the secondsource-sense-terminal conductor layer 109 by a wire 122A, as shown inFIG. 8 by a two-dot chain line. In this case, as shown in FIG. 9 by atwo-dot chain line, each fourth connection metal member 220 can beconnected to the fourth source-sense-terminal conductor layer 209 by awire 122B, and at the same time, the fourth source-sense-terminalconductor layer 209 can be connected to the second source-sense-terminalconductor layer 109 by a wire not shown.

While the embodiments of the present invention are described in detail,these are only specific examples used for clarifying technical contentsof the present invention, and the present invention should not beconstrued as being limited to these specific examples, but is onlylimited by the scope of the appended claims.

This application corresponds to Japanese Patent Application No.2013-240105 filed in Japan Patent Office on Nov. 20, 2013, the entiredisclosure of which is incorporated herein by reference.

DESCRIPTION OF SYMBOLS

-   -   1 switching device    -   2 resin package    -   3 source terminal    -   4 sense source terminal    -   5 gate terminal    -   6 drain terminal    -   11 semiconductor chip    -   12 drain pad    -   13 source pad    -   14 gate pad    -   16 source wire    -   17 sense source wire    -   19 MOSFET    -   22, R1 to R4 external resistances    -   31 inverter circuit    -   32 first switching device    -   33 second switching device    -   34 third switching device    -   35 fourth switching device    -   40 control section    -   41 power supply    -   42 load    -   51 amplifier circuit    -   52 first switching circuit    -   53 gate resistance    -   54 second switching circuit    -   55 current blocking resistance    -   56 overcurrent detection circuit    -   57 current detecting resistance    -   58 comparison circuit    -   59 voltage monitoring portion    -   61 semiconductor module    -   Tr1 to Tr4 switching elements    -   Di1 to Di4 Di1 to Di4

1-8. (canceled)
 9. An electronic circuit including: a switching device;an overcurrent detection circuit for detecting that an overcurrent isflowing through the switching device; and an overcurrent protectioncircuit for blocking the current flowing through the switching devicewhen an overcurrent is detected by the overcurrent detection circuit,wherein the switching device comprises a switching element which has afirst electrode, a second electrode and a third electrode and in whichon-off control is performed between the second electrode and the thirdelectrode by applying a drive voltage between the first electrode andthe second electrode in a state where a potential difference is appliedbetween the second electrode and the third electrode; a drive terminalelectrically connected to the second electrode for applying the drivevoltage; and an external resistance that is interposed in a current pathbetween the drive terminal and the second electrode, is separated fromat least one of the drive terminal and the second electrode, and has apredetermined resistance value.
 10. The electronic circuit according toclaim 9, including: an output terminal for outputting a current flowingby the on control; and a conductive member connecting the outputterminal and the second electrode, wherein the external resistanceincludes the conductive member.
 11. The electronic circuit according toclaim 10, wherein the conductive member includes a bonding wirestretched between the output terminal and the second electrode.
 12. Theelectronic circuit according to claim 9, including: a resin packagesealing the switching element, the drive terminal and the externalresistance.
 13. The electronic circuit according to claim 9, wherein thefirst electrode is a gate electrode, the second electrode is a sourceelectrode, the third electrode is a drain electrode, and the driveterminal is a sense source terminal.
 14. The electronic circuitaccording to claim 9, wherein the first electrode is a gate electrode,the second electrode is an emitter electrode, the third electrode is acollector electrode, and the drive terminal is a sense emitter terminal.15. The electronic circuit according to claim 9, wherein the firstelectrode is a base electrode, the second electrode is an emitterelectrode, the third electrode is a collector electrode, and the driveterminal is a sense emitter terminal.
 16. The electronic circuitaccording to claim 9, wherein the predetermined resistance value is setso as to reduce a voltage drop at the external resistance when a firstcurrent flowing between the second electrode and the third electrode isrelatively small or is a rated value than when the first current isgreater than the rated value, such that a reduction of the voltageapplied between the first electrode and the second electrode can besuppressed, and a drive voltage necessary and sufficient for a switchingoperation can be fed to the switching element.
 17. The electroniccircuit according to claim 16, wherein the resistance value of theexternal resistance is set to ID×1/100 mΩ to 5×ID×1/100 mΩ, wherein IDis the first current.
 18. The electronic circuit according to claim 13,wherein the switching element is SiC MOSFET.